Actually, I have never owned a MP3 player device (not much into music). How are they less simple than even current generation of e-book readers?

You very likely typed that message on an MP3 player device. (With a lot of extra features.) One that creates MP3s from CDs.

Ebooks can't be easily created & read on computers by people who own pbooks; there's a much steeper barrier to the switch from pbook to ebook.

Most (pre-packaged?) computers have mp3 player programs pre-installed; they don't have ebook reading programs installed (and that's before we get into the format wars). They certainly don't have ebook *creation* software pre-installed.